Process and apparatus for emptying low temperature liquefied gases from tanks and tankers



Jan. 5, 1965 B KER 163,992

R. EC PROCESS AND APPARATUS FOR EMPTYING LOW TEMPERATURE LIQUEFIED GASES FROM TANKS AND TANKERS Filed June 24, 1963 sz RI {IIIIE I ll l '1 I 'il l l I ll ln E\ D'' I I III! I l I I n =E ll I I' 'l I l l l $2 X i I I l a? I l I I i 1 a a lnven/or RUDOLF BECKER Afro/0W5 United States Patent 35,38 Claims. (61. 6255) This invention relates to a method and apparatus for emptying extremely cooled liquefied gases, especially fuel gases such as methane, from stationary and mobile tanks, particularly from tankers.

The withdrawal of liquefied gases from tankers, which of course, frequently travel over long distances, has heretofore been accomplished in general by means of pumps mounted in the holds of the ships. Submerged pumps have also been used, which were mounted inside the tanks and driven by motors on top of the tanks through long shafts. Each tank would then require an operating pump and a reserve pump. If, for example, a tanker has 20 tanks, 40 low temperature pumps would have to be installed inside the ship. The pump rooms would also, therefore, be in great danger of being contaminated by poisonous and explosive gases.

If the tanks are emptied by compressed gases at normal temperature, then at the end of the process the tanks will be filled with warm gases on the one hand, and residual amounts of cold liquid on the other hand, which combination will produce undesired thermal stresses. Also, the provision of so-called pressure gas introduction systems requires piping in the bottoms of the tanks which is not readily accessible and is subject to breakage due to thermal stresses.

The principal object of this invention, therefore, is to provide a novel method for emptying low temperature liquefied gases from containers, which method substantially avoids the disadvantages of prior systems.

Another object is to provide novel apparatus for accomplishing the method of the present invention.

Upon further study of the specification and claims, other objects and advantages of the present invention will become apparent.

The attached drawing presents, in schematic flow sheet form, the preferred embodiment of this invention.

The objects of this invention are attained by a system characterized by the use of gas pressure to expel the liquid, in particular, by the formation of gas from the cold liquid in the tank and at substantially the same (slightly higher) temperature than the liquid. The pressure of the accumulated gas over the liquid will force the liquid into the open end of a pipe at the bottom of the tank and from there into a collection conduit at the top of the tank, from which either evaporated gas is withdrawn or liquefied gas is delivered by gravity or pumps to the tanks to be filled.

Since the gas that is allowed to accumulate in order to expel the liquid is at about the same temperature as the liquid, thermal stresses do not occur. Furthermore, by positioning the collection conduit above the tank that is being emptied, there is obviated the employment of relatively inaccessible pumps and associated piping which were common disadvantages in prior systems.

(In this connection, it is believed worthy to note that a piping failure is suspected by authorities as the cause of the tragedy to the ill-fated submarine U.S.S. Thresher. The present invention, therefore, is an important contribution which fulfills a long-felt need as by the employment of this inventtion there are avoided to a large extentthose 3,163,%2 Patented Jan. 5., 1965 hazards resulting from high pressure piping systems carrying toxic and explosive substances.)

As a further development of this invention, the pressure at the bottom of the tank is kept constant during the emptying of the tank by using a throttle valve to control the amount of gas that is left in the tank for warming or expelling the liquid. In this manner the conditions under which the tank is being emptied will be independent of the level of the liquid in the tank.

Any gas that accumulates in the discharge conduit during the emptying of the tanks can be advantageously conducted to a gasometer.

According to a comprehensive method of practicing this invention, some or all of the gas which has accumulated in the piping l) is preheated by heat exchange preferably with water, (2) is compressed, (3) is condensed in an indirect heater inside the tank while a corresponding portion of the liquid in the tank is being evaporated, and (4) after such condensation is returned in the liquid state to the collection conduit on top of the tank through a throttle valve that is controlled by the pressure at the bottom of the tank.

Any surplus gas which exceeds the requirements of the heater is preferably diverted to a by-pass pipe containing a pressure relief valve for preventing the pressure from exceeding the maximum allowable value which is usually between 4 and 5 atmospheres (gage). Surplus gas is then recycled to the suction side of the compressor. (The maximum pressure of 4 and 5 atm. (gage) is for liquefied gases such as methane.)

In another form of this invention the heater in the tank can be heated by gas from another source so as to evaporate from the liquid in the tank the gas that is necessary to expel the liquid. As a separate gas for this purpose, it is advantageous to use liquefiable propane.

According to still another embodiment of this invention, a relatively small amount of liquid is placed under the required pressure by means of a pump, then vaporized by heat exchange, preferably with water, and the resulting gas introduced directly into the tanks to force out their liquid contents.

Whether a small quantity of liquid is completely vaporized outside or inside the tank, the composition of the gas will be substantially the same as the liquid, any distillation effects being considered within this definition.

Under some conditions it is also advantageous to preheat, preferably with Water, some gas that is obtained either from the collection conduit or by evaporation of a small amount of the liquid, and to introduce this preheated gas directly into the liquid at the bottom of the tank. During its migration through the liquid the gas thus introduced will be cooled almost down to the temperature of the liquid, and after collecting in the upper part of the tank it can serve to press the liquid from the tank into the collection conduit.

Referring now to the drawing, the insulated liquefied gas tank 1 is connected with a collection conduit 3 by means of a collection pipe 2 which opens at the bottom of the tank. From the top of the collection conduit a pipe 4 leads to a heat exchanger 5 through which water is circulated. After traversing this heat exchanger the pipe 4 joins the pipe 6 which leads to the compressor '7. From the high pressure side of the compressor the pipe 8 leads into the tank 1 to the heater 9, from which the pipe It) delivers the condensate to the throttle valve 11 and returns it from there to the collection conduit 3. The throttle valve 11 is automatically controlled by the pressure at the bottom of the tank as indicated by the dotted line 12. The pressure pipe 8 has connected to ita branch pipe 13 leading to the relief valve 14 which is controlled by the pressure in pipe 8, as indicated by dotted lines,

a said pressure being preferably between 4 and 5 atmospheres. After leaving the valve 14, the gas which is not needed for the heater 9 is delivered to pipe 4 for return to the suction side of the compreswr.

Another branch pipe 16 leading from pipe 4 is connected to a gasometer 17.

From the bottom of the collection conduit 3 a pipe 18 leads to a pump 19 which sends the liquefied gas through pipe 20 to a storage tank 21. From the pressure pipe 20 a branch pipe 22 leads to a throttle valve 23 and from there back again to the collection conduit 3. As indicated by dotted lines, the throttle valve 23 is controlled by the liquid level in the collection conduit 3, which eliminates the necessity of providing an emptying pump for said collection conduit 3.

A gas escape pipe 25 connects the gas space at the top of tank 1 with a safety valve 26 which is preferably controlled by the pressure at the bottom of the tank, as indicated by dotted lines.

The pressure at the bottom of the tank is equal to the liquid columns H +H and is maintained during the entire emptying process. A liquid level of height H always remains in the tank so that a certain ballast will be present during the return trip of the tanker. With this procedure the gas pressure in the tank will have to be increased While the liquid level is being lowered in order to keep the total pressure H +H constant.

The relief valve 26 connected by pipe 25 with the gas space in tank 1 is in this invention controlled by the pressure in the bottom of the tank for reasons of safety because if the gas in the tank would 'be under constant pressure, then the tank would have to be made stronger to support the total load when it is full of liquid, which would greatly increase its cost.

The system here described makes it possible to empty quickly and conveniently a plurality of liquid gas tanks by the use of only a single compressor '7 for which only a single reserve aggregate is necessary. The collection conduit 3 being above the tank is readilyaccessible at all times While the pump 19 can be located in a place where there will be no harmful or dangerous accumulation of gases.

While it is readily apparent that this invention is applicable to the delivery of any liquid from any container, it is to be appreciated that it is most valuable in the emptying of liquids having normal boiling points less than C.

From the foregoing description, one skilled inthe art can easily ascertain the essential characteristics of this invention, and without departing from the spirit and scope thereof, can make various changes and modifications of the invention to adapt it to various usages and conditions. Consequently, such changes and modifications are properly, equitably, and intended to be, within the full range of equivalence of the following claims.

What is claimed is:

1. A method of emptying liquefied gas from a tank, preferably a tanker, which method comprises; generating a gas in a liquid storagetank having substantially the same or only a little higher temperature than the liquid accumulating above the liquid at such a higher pressure that the liquid is expelled from the bottom zone of the tank up through the tank and is collected above the tank in a collection zone from which vaporized gas can be withdrawn and liquid can be delivered to other or onshore tanks; withdrawing the vaporized gas from the collection zone, heating the withdrawn vaporized gas compressing the heated gas, passing at least a portion of the compressed gas in indirect heat transfer relationship with the liquid in the tank, thereby vaporizing the liquid into said gas; further condensing the compressed gas which is passed in indirect heat transfer relationship with the liquid in the tank, passing the condensed gas out of the tank through a throttle valve, and delivering the condensed gas from the throttle valve to the collection zone.

2. The method of claim 1, further comprising passing the other portion of the compressed gas by a pressure relief valve to join the gas Withdrawn from the collection zone before it is compressed.

3. A method of emptying liquefied gas from a tanker, which method comprises; introducing a gas into a tanker containing liquid gas and in direct contact with said liquid, said gas being at substantially the same temperature, having substantially the same composition and having a higher pressure than the liquid; permitting the gas to accumulate above the liquid; and collecting the liquid that is expelled from the tanker, said expelled liquid coming from the bottom zone of the tanker up through the tanker and being collected above the tanker in a collection zone, withdrawing the liquid from the collection zone and delivering it to on-shore storage tanks, withdrawing the vaporized gas from the collection zone, heating the withdrawn vaporized gas, compressing the heated gas, passing at least a portion of the compressed gas in indirect heat transfer relationship with the liquid in the tanker thereby vaporizing the liquid into said gas which is introduced into said liquid, condensing the compressed gas which is passed in indirect heat transfer relationship with the liquid in the tanker, passing the condensed gas out of the tanker through a throttle valve, adjusting said throttle valve in response to the pressure at the bottom of the tanker, and delivering the condensed gas from the throttle valve to the collection zone.

4. A method of emptying liquefied gas from a tank, preferably a tanker, which method comprises; passing a gas, such as propane, from an external source and at a higher temperature than the liquid in the tank in indirect heat exchange relationship with the liquid in the tank, thereby vaporizing a liquid in the tank into a gas having substantially the same or only a little higher temperature than the liquid and accumulating above the liquid at such a higher pressure that the liquid is expelled from the bottom zone of the tank up through the tank and is collected above the tank in a collection zone from which vaporized gas can be withdrawn and liquid can be delivered to other or on-shore tanks; passing the gas from the external source after being cooled or condensed by heat exchange relationship with the liquid in the tank out of the tank through a throttle valve, adjusting said throttle valve in response to the pressure at the bottom of the tank, and delivering the cooled or condensed gas from the throttle valve to further external use or back in a closed circuit to be further used as heating gas.

5. A method of emptying liquefied gas from a tank, preferably a tanker, which method comprises; pumping a small quantity of the liquid from the tank under an increased pressure, heating the compressed liquid by heat exchange relationship with a heating medium such as water to vaporize said liquid and passing said vaporized gas by way of a throttle valve into the bottom zone of the tank, adjusting said throttle valve in response to .the pressure at the bottom of the tank, said gas accumulating above the liquid at substantially the same or only a little higher temperature than the liquid and at such a higher pressure that the liquid is expelled from the bottom zone of the tank up through the tank, and is collected above the tank in a collection zone from which vaporized gas can be withdrawn and liquid can be delivered to other or on-shore tanks.

6. Apparatus for emptying liquid from a tank, which apparatus comprises:

(a) enclosed tank means;

(b) a pipe having an upper and lower end, said lower end being open and disposed in the bottom of the interior of said tank means;

(c) collection conduit means being disposed above said tank means and being in communication with the upper end of said pipe, said collection conduit means having a lower space for liquid and an upper space for gas;

((2) indirect heat exchange means having an inlet and an outlet, said inlet being in communication with the upper space of said collection conduit;

(2) compressor means having a suction side and a pres sure side, the suction side being in communication with the outlet of said indirect heat exchange means;

(f) heater means for vaporizing liquid in said tank means, said heater means being disposed in the interior of said tank, and being in communication with the pressure side of the compressor;

(g) a second pipe being connected from the heater means to the gas space of said collection conduit means; and

(h) throttle valve means being disposed in the second pipe and being adjustably responsive to the pressure at the bottom of said tank.

7. The apparatus of claim 6, further comprising bypass means disposed between the pressure side of the compressor means and the inlet side of the heat exchange means, said by-pass means having pressure relief valve means integral therewith.

8. The apparatus of claim 6, further comprising a conduit connected between the upper space of the collection conduit means and a gasometer.

9. The apparatus of claim 6, further comprising pump means having an inlet and an outlet, said inlet being in communication with the lower space of the collection conduit means; pressure pipe means communicating with the outlet of said pump and an onshore tank; branch pipe means connected between said pressure pipe means and the upper space of said collection conduit means, said branch pipe means containing a throttle valve adjustably responsive to the liquid level in the collection conduit means.

10. The apparatus of claim 6, further comprising safety valve means connected to the top of said tank means and responsive to the pressure at the bottom of said tank.

References Cited by the Examiner UNITED STATES PATENTS 1,943,059 1/34 Dana 6253 1,950,353 3/34 Dana 6251 2,296,598 9/42 Cook 62-55 2,443,724 6/48 Cibulka 6251 2,576,985 12/51 Wildhack 6251 2,971,345 2/61 Ball 6253 3,018,634 1/62 Gilmore 6252 3,097,497 7/63 Fitt 6252 ROBERT A. OLEARY, Primary Examiner. 

1. A METHOD OF EMPTYING LIQUEFIED GAS FROM A TANK, PREFERABLY A TANKER, WHICH METHOD COMPRISES; GENERATING A GAS IN A LIQUID STORAGE TANK HAVING SUBSTANTIALLY THE SAME OR ONLY A LITTLE HIGHER TEMPERATURE THAN THE LIQUID ACCUMULATING ABOVE THE LIQUID AT SUCH A HIGHER PRESSURE THAT THE LIQUID IS EXPELLED FROM THE BOTTOM ZONE OF THE TANK UP THROUGH THE TANK AND IS COLLECTED ABOVE THE TANK IN A COLLECTION ZONE FROM WHICH VAPORIZED GAS CAN BE WITHDRAWN AND LIQUID CAN BE DELIVERED TO OTHER OR ONSHORE TANKS; WITHDRAWING THE VAPORIZED GAS FROM THE COLLECTION ZONE, HEATING THE WITHDRAWN VAPORIZED GAS COMPRESSING THE HEATED GAS, PASSING AT LEAST A PORTION OF THE COMPRESSED GAS IN INDIRECT HEAT TRANSFER RELATIONSHIP WITH THE LIQUID IN THE TANK, THEREBY VAPORIZING THE LIQUID INTO SAID GAS; FURTHER CONDENSING THE COMPRESSED GAS WHICH IS PASSED IN INDIRECT HEAT TRANSFER RELATIONSHIP WITH THE LIQUID IN THE TANK, PASSING THE CONDENSED GAS OUT OF THE TANK THROUGH A THROTTLE VALVE, AND DELIVERING THE CONDENSED GAS FROM THE THROTTLE VALVE TO THE COLLECTION ZONE. 